Mask blanks inspection tool

ABSTRACT

Embodiments include determining whether defects exist in an extreme ultraviolet (EUV) light mask blank. Incident EUV light scattered or diffused by abnormalities in the layers of the mask blank may be measured, normalized, and compared to threshold values to determine if and where a defect exists. Normalizing may be performed by dividing a light intensity value for a pixel by the average of light intensity values for one or more rings of surrounding pixels. A defect may be determined by considering whether the normalized intensity value for a pixel is greater than a pixel threshold to identify the pixel is a candidate for a location with a defect; and by determining whether the sum of normalized light intensity values for a block of pixels including the pixel satisfies a pixel block threshold to determine whether the block scatters or diffuses a critical amount of light to identify a defect.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/971,786 filed Oct. 21, 2004 now U.S. Pat. No. 7,005,649, which claimsthe benefit of the earlier filing date of co-pending JapaneseApplication No. 265399/2004, filed Sep. 13, 2004, by Intel Corporation,titled “Mask Blanks Inspection Method and Mask Blank Inspection Tool”.

BACKGROUND

1. Field

Circuit patterning and more particularly to masks used to pattern lightsensitive material on substrates or wafers.

2. Background

Patterning is the series of operations that results in the removal ofselected portions of surface layers added on a substrate, such as awafer. Patterning creates the surface parts of devices that make-up acircuit. One goal of patterning is to create in or on the wafer surface,the parts of the device or circuit in the exact dimensions (featuresize) required by the circuit design and to locate the parts in theirproper location on the wafer surface.

Generally, patterning is accomplished through photolithographytechniques. For example, photolithography may be a multi-operationpattern transfer process wherein a pattern contained on a reticle, photomask, etch mask, or multi-layers mask is transferred onto the surface ofa wafer or substrate through a lithographic imaging operation, and alight sensitive material (e.g., photoresist) is developed on the wafer.One goal of circuit designers is to reduce the feature size (thecritical dimension) of devices of a circuit, i.e., reduce the smallestfeature patternable. A reduction in wavelength of light used inpatterning will reduce the critical dimension. Thus, the patterningwavelength can be reduced to under 200 nanometers, and can lie in theextreme ultraviolet (EUV) light region to reduce the critical dimensionto 100 nanometers or less.

In the general course of patterning, the image of a reticle or photomask is projected onto a wafer or substrate surface by an imagingsystem. EUV light radiation, however, does not pass through quartz orglass, and is therefore typically projected using reflective optics. Forexample, a reticle or photo mask for EUV light patterning of a lightsensitive material may include a multi-layer mask that is created byforming light absorbing material on certain portions of a substratecovered with multiple layers of a reflective material (e.g., apatterning mask). The substrate having only multiple layers ofreflective material may be referred to as a “mask blank” (e.g., such asa substrate having multiple layers of reflective material, prior toforming the light absorbing material).

It is important to be able to inspect an EUV light mask blank fordefects that may cause errors in the imaging or patterning of the lightsensitive material, such as by causing unwanted variations in the imageof features (e.g., such as critical features) patterned on that materialby the patterning mask formed from that mask blank. Specifically,because of the wavelength of EUV light used to expose the lightsensitive material, a small bump with a height as low as two nanometerson the surface of a multi-layered mask blank may cause errors in theimaging or patterning of the light sensitive material, and thus be adefect in the mask blank. Therefore, EUV light patterning photo maskblanks may be inspected during manufacture, after manufacture, prior toshipment, or after shipment to detect “critical defects” (e.g., such asdefects that may cause an error in patterning) while minimizingdetection of “false defects” (e.g., such as defects that do not causeerrors in patterning substantial enough to affect the critical dimensionof features to be formed).

BRIEF DESCRIPTION OF THE DRAWINGS

Various features, aspects and advantages will become more thoroughlyapparent from the following detailed description, the set of claims, andaccompanying drawings in which:

FIG. 1 is one embodiment of a system for inspecting a multi-layered maskblank.

FIG. 2 is a cross-sectional view of a multi-layered mask blank.

FIG. 3 is a top perspective view of a multi-layered mask blank.

FIG. 4 is a top perspective view of a multi-layered mask blank.

FIG. 5 is a flow diagram of a process for locating defects in amulti-layered mask blank.

DETAILED DESCRIPTION

FIG. 1 is one embodiment of a system for inspecting multi-layered maskblanks. FIG. 1 shows system 100 having source 110 to illuminatesubstrate 105. Source 110 may provide (e.g., reflect) incident light ILto substrate 105 using source mirror 112 (e.g., such as a sphericalmirror or aspherical mirror). Light from source 110 may be focused bysource mirror 112 onto surface 115 of substrate 105, below surface 115of substrate 105, or above surface 115 of substrate 105.

In addition, source 110 may be an illumination apparatus, such as asource of light, ultraviolet (UV) light, extreme ultraviolet (EUV)light, or other light appropriate for patterning a light sensitivematerial on a substrate or wafer, or for inspecting an etch orpatterning mask blank. Accordingly, source 110 may provide light havinga wavelength in the range of 10 to 400 nanometers (e.g., UV light), suchas by providing light having a wavelength of 20 nanometers, 50nanometers, 100 nanometers, 150 nanometers, or 175 nanometers.Specifically, source 110 may produce light such that incident light ILis EUV light having a wavelength of between 10 nanometers and 200nanometers, such as by having a wavelength of 11 nanometers, 12nanometers, 13 nanometers, 13.5 nanometers, 14 nanometers, 15nanometers, or 16 nanometers. In addition, light source 110 may includea filter, such as a filter to ensure that the wavelength or incidentlight IL is in a desired range, such as within the EUV range of 10 nm to200 nm, as specified above.

Substrate 105 may be a substrate or wafer including multiple layers of areflective material, a multi-layered patterning mask, a patterning mask,an etch mask, a lithographic mask, a photolithography mask, a photomask, or a mask blank thereof. Thus, it is contemplated that source 110and source mirror 112 are sufficient to illuminate bumps orirregularities in the height of surface 115 or layers below surface 115of substrate 105. For instance, substrate 105 may be a plate orsubstrate having multiple layers of reflective material of molybdenum(Mo) and silicon (Si) formed thereon, and source 110 may provideincident light IL having an appropriate wavelength, intensity, and focusto illuminate or penetrate all of the layers of Mo and Si formedthereon.

Thus, substrate 105 may be a patterning or etch mask blank, such as asubstrate or plate having multiple layers of molybdenum (Mo) or silicon(Si) formed thereon in an alternating layered order, where surface 115is the surface of a top layer of molybdenum (Mo) or silicon (Si), priorto the mask blank having a buffer layer and absorber layer deposited onsurface 115. Specifically, surface 115 may have a buffer layer formedthereon; an absorber layer formed on the buffer layer; a patternpatterned, written, or etched in the absorber layer; and then have apattern written or etched into the buffer layer (e.g., to form apatterning mask). It is also to be appreciated that this process mayinclude repair of the absorber layer (such as during patterning,writing, or etching). Thus, substrate 105 may be a mask blank of a maskto be formed for patterning or etching a silicon wafer, such as a waferon which electronic semiconductor devices are being formed, using EUVpatterning of a light sensitive material formed or layered on the wafer.

It is also contemplated that substrate 105 may have between 10 and 60layers (e.g., such as by having between 10 and 60 layers of Mo and Simaterial). For example, substrate 105 may include 20, 25, 30, 35, 40,45, or 50 layers of Mo and Si material where each layer is one layer ofeither Mo or Si material of an alternating Mo Si layer structure. Inaddition, each of the Mo or Si layers may be a reflective layer, such asa layer capable of partially reflecting EUV light. For example, incidentlight IL may penetrate all of the multi-layers of substrate 105 (e.g.,such as by penetrating 35, 40, or 45 layers of Mo and Si without beingcompletely absorbed and/or reflected by those layers).

Because the EUV light can have light intensity spread over a lightfrequency bandwidth (e.g., such as by having light intensity across abandwidth of frequencies as large as about two percent of the selectedor desired frequency of the light), it is useful to describe thefrequency of EUV light, such as incident light IL, in terms of “centroidwavelength”. A centroid wavelength may represent a wavelength at whichis located the mean value across the bandwidth of the intensity of EUVlight used or radiated.

According to embodiments, source 110 may generate incident light ILhaving an EUV light whose centroid wavelength is between 1.005 and 1.010times the centroid wavelength of a light used to pattern or exposeportions of a light sensitive material on a wafer during aphotolithographic process where portions corresponding to a patternformed on substrate 105 of reflective multi-layers (as compared to lightabsorbing material formed on the reflective multi-layers) are formed inthe light sensitive material of the wafer. For example, incident lightIL may have a centroid wavelength of 1.006, 1.007, 1.008, or 1.009 timesa centroid wavelength of a patterning light used to expose portions oflight sensitive material on a wafer being patterned with a patterningmask formed from the mask blank being inspected by incident light IL.

Moreover, it is considered that the light used to expose the lightsensitive material on the wafer may be incident upon surface 115,substrate 105, and/or the light sensitive material of the wafer at anangle of between six degrees and eight degrees from perpendicular tosurface 115 (e.g., such as by being at an angle of between 6 degrees and8 degrees from axis AX of mirror 120, as shown in FIG. 1). For example,the patterning light used to expose the light sensitive material on thewafer may be incident at an angle of 6.5 degrees, 7 degrees, or 7.5degrees from axis AX.

FIG. 1 also shows scattered light SL such as dark-field, imaging lightscattered, diffused, or reflected from substrate 105. Specifically,scattered light SL may include reflected light, scattered light,diffused light, caused by illumination of multiple Mo and Si layers ofsubstrate 105 by incident light IL. However, according to embodiments,scattered light SL may exclude a portion of or all of specularreflection of incident light IL from substrate 105. Thus, according toembodiments, incident light IL may be completely reflected by layers ofreflective material that are part of substrate 105 (e.g., such as layersof Mo or Si material formed on a substrate or plate as describedherein). Specifically, incident light IL may be reflected, scattered, ordiffused by the layer that forms surface 115 of substrate 105 as well asone or more layers of multi-layer material of substrate 105 belowsurface 115 (e.g., such as multiple layers of Mo and Si material onwhich a surface layer of Mo or Si is formed).

Furthermore, according to embodiments, scattered light SL may include aportion or all of incident light IL reflected, scattered, or diffused bysubstrate 105. Thus, when incident light IL encounters a bump orirregularity on or below surface 115, the magnitude or brightness ofscattered light SL may increase while the magnitude or brightness ofspecular reflection decreases.

Mirror 120 may be used to gather all or a portion of scattered light SL.Mirror 120 may be a spherical mirror having perimeter P1 (e.g., such asa diameter) and opening OP. In addition, mirror 120 may be designed toreflect scattered light SL to mirror 130. Mirror 130 may also be aspherical mirror having perimeter P2 (e.g., such as a diameter) smallerthan perimeter P1. Mirror 130 may be designed to reflect a portion orall of the scattered light received from mirror 120 to a detector. Forexample, mirror 130 may reflect that light through opening OP todetector 140.

According to embodiments, mirror 120 and mirror 130 may be mirrorshaving a spherical shape including less than 20% of a sphere by surfacearea. Specifically, mirror 120 may have a numerical aperture (NA) of 0.2and have a concave spherical shape. Likewise, mirror 130 may have an NAof 0.1 and have a convex-shaped spherical reflective surface.

Furthermore, according to embodiments, opening OP may have a diameterless then or equal to perimeter P2 of mirror 130. More particularly,opening OP (e.g., such as a diameter of opening OP) may be larger thanthe trace or cross-sectional shape of a light ray which is reflected atthe edges or perimeter P2 of mirror 130. Mirror 120, mirror 130, andopening OP may be part of a “Schwarzschild Optics” device.

Detector 140 may be a device for detecting light, such as UV or EUVlight. For example, detector 140 may be a camera or electronic-typeimage sensing array (ISA), such as a charge-coupled device (CCD), orvarious other appropriate pixel imaging technology able to capturescattered light reflected to detector 140.

As shown in FIG. 1, source mirror 112 may be aligned or disposed alongaxis AX of mirror 120. Similarly, detector 140 may be oriented ordisposed along axis AX. Moreover, axis AX may be oriented perpendicularto surface 115 of substrate 105. Also, it is considered that there maybe angle AN between the outermost ray of the illumination of incidentlight IL or the half cone angle of the illumination of incident light ILand surface 115. In one case, angle AN may be between 85 and 90 degrees,such as by being 86 degrees, 87 degrees, 88 degrees, or 89 degrees.

FIG. 1 also shows moving apparatus 160 attached to substrate 105. Movingapparatus 160 may be an apparatus sufficient to move surface 115 inthree dimensions with respect to axis AX. For example, FIG. 1 shows axes170 having an “X” axis and a “Y” axis forming a two dimensional planethat may be parallel to surface 115. Thus, moving apparatus 160 may movesurface 115 along the “X” “Y” plane of axes 170, in two dimensions withrespect to axis AX. Specifically, moving apparatus 160 may movesubstrate 105 with respect to incident light IL so that incident lightIL is incident upon all or a portion of surface 115. Moreover, movingapparatus 160 may move substrate 105 so that source mirror 112, mirror120, and detector 140 are oriented or disposed along axis AX at an anglewith respect to surface 115 as described above (e.g., such as where axisAX is oriented perpendicular to surface 115).

In addition, to focus the Schwarzschild Optics with respect to substrate105 (e.g., such that the focus of mirror 112 and/or mirror 120 are atsurface 115, or at a desired depth below surface 115), moving apparatus160 may move substrate 105 along axis AX (e.g., the third dimension withrespect to axis AX) so that source mirror 112, mirror 120, and detector140 are oriented or disposed along axis AX (e.g., such as by thosedevices being located along axis AX at an appropriate distance fromsurface 115 to focus one or more of the mirrors as desired).

According to embodiments, moving apparatus 160 can be a servo stage thatcan have a mask blank set on it and that can be controlled by acomputer. For instance, moving apparatus 160 may have a platform orsurface on which substrate 105 is placed or attached (e.g., such asremovably attached by physical restraints or adhesive). Moving apparatusmay further include one or more servos, that are controlled by acomputer (e.g., such as according to a machine accessible medium havinginstructions for execution by a machine, or a software routine), to movethe substrate in three dimensions, as described above.

In addition, system 100 or components thereof may exist in a vacuumsetting, for example, light provided by source 110, incident light IL,substrate 105, scattered light SL, mirror 120, mirror 130, and lightreflected by mirror 130 to detector 140 may exist in a vacuum sufficientto allow for propagation of EUV light sufficient for systems andprocesses described herein. Thus, it can be appreciated that system 100,substrate 105, multiple layers of reflective material on substrate 105(e.g., such as alternating layers of Mo and Si formed on and belowsurface 115) and a patterning mask formed from substrate 105 (e.g., suchas where substrate 105 is a mask blank) may be designed, configured, anduse optics and pressure appropriate for transmission of EUV light). Forinstance, those devices may be designed without lenses or glass throughwhich the EUV light is to pass (e.g., since EUV light does not passthrough glass) and may be designed to only have the EUV light travel ina vacuum (e.g., since EUV light does not travel far in an atmospheresuch as air).

As noted above, incident light IL may gradually penetrate, be reflectedby and/or be absorbed by the multiple layers of substrate 105. Forexample, FIG. 2 is a cross-sectional view of a multi-layered mask blank.FIG. 2 shows substrate 105 having substrate 205 and first layer L1,second layer L2, third layer L3, fourth layer L4, and fifth layer L5formed on top of substrate 205. As mentioned above, it is contemplatedthat substrate 105 may include between 10 and 60 layers, thus layers L1through L5 may be representative of a portion of the total layers of amulti-layer mask blank. As shown in FIG. 2, surface 115 is the surfaceof fifth layer L5. Thus, incident light IL, incident upon substrate 105,may be scattered or diffused by defect DEF1 which has form bump B1 abovesurface 115, such as is shown by scattered light SL1 in FIG. 2.Similarly, where incident light IL is EUV light, defect DEF2 may scatteror diffuse EUV light EUV by causing deformations or bumps in layers L1through L5, such as is shown by SL2 in FIG. 2.

Thus, system 100 of FIG. 1 may be able to detect-abnormalities, bumps,or defects within the layers of substrate 105, by using dark-fieldimaging optics to gather the scattered, reflected, or diffused lightresulting from the abnormalities, bumps, or defects in the multiplelayers resulting from the defect. It is contemplated that system 100 maybe able to detect defects having a height between 2 nanometers (nm) and8 nanometers in height (e.g., see height H of defect DEF2 of FIG. 2),and having a width of between 35 nm and 94 nm (such as width W of defectDEF2 as shown in FIG. 2). For instance, a defect having a height andwidth as described above may cause abnormalities, bumps, or defects inthe planarity of the multiple layers of the mask blank, thus causingdiffusion or scattering of EUV light incident upon those layers. Thescattered or diffused light may be gathered, measured or detected bysystem 100 such as by mirrors 120 and 130, which reflect scattered lightSL to detector 140, which measures the intensity or amount of thescattered light. It can be appreciated that such defects may be a bumpor abnormality at or below surface 115 (e.g., such as a defect or bumpof unwanted material or space within the layers of substrate 105).

For instance, system 100 of FIG. 1 may detect a defect having a width ofbetween 60 to 70 nm, and a height of 2 nm or greater as a criticaldefect. Thus, apparatus 100 may be able to detect a defect at anapproximate lower-layer level, such as at layers 35-40 below surface 115of 40 layers, having a 60 nm width and a height of 2 nm or greater, thatforms a bump of between 0.4 and 2.3 nm in height at surface 115.Likewise, apparatus 100 may detect a defect at an approximate mid-layerlever, such as at layer 15 below surface 115 of 40 layers, that createsa bump at surface 115 of 2.3 nm in height.

Specifically, as shown in FIG. 2, system 100 may be able to detect,identify, and locate defect DEF2 having height H of 3 nm, 4 nm, 5 nm, 6nm, or 7 nm and producing bump height B2 of zero or more nanometers atsurface 115 by measuring scattered light SL2 reflected by layers L1through L5 of substrate 105 when those layers are illuminated byincident light IL2. Similarly, system 100 may detect, identify, andlocate defect DEF1 having bump height B1 of 2 nm, 2.5 nm, 3 nm, or 4 nmat surface 115 by measuring scattered light SL1 resulting fromilluminating substrate 105 and defect DEF1 with incident light IL1.

FIG. 1 also shows logic 150 connected to detector 140. For example,logic 150 includes logic circuitry, gates, computer logic hardware,memories, comparators, and/or registers coupled to detector 140 todetermine whether reflective, scattered, or diffused light received andmeasured from substrate 105 satisfies a criteria. Thus, logic 150 mayinclude logic to detect, identify, and locate defects in substrate 105(e.g., such as defects within the multiple layers of a multi-layer maskblank as described above with respect to FIG. 2). Specifically,“detecting” a defect as used herein may include measuring reflectedlight intensity values and normalizing those values for a number ofpixels, as described herein. Also, “identifying” a defect as used hereinmay include determining whether the measured and normalized value ofreflective light from the pixels satisfies criteria to indicate that adefect exists, such as described herein. Next, “locating” a defect asused herein may include determining a location of a defect, such as alocation at one or more pixels where the defect exists, as describedherein.

In one instance, logic 150 may determine whether a pixel threshold valueis satisfied by a pixel reflective light intensity value received bydetector 140 for a first pixel of substrate 105, where substrate 105 isa multi-layered patterning mask blank. It is considered that the pixelreflective light intensity value received by detector 140 may benormalized as described below with respect to FIG. 3, prior to logic 150determining whether the threshold value is satisfied. For example, logic150 may determine whether the normalized scattered light intensity valueat center pixel CP is greater than a pixel threshold value, thusidentifying center pixel CP as a candidate for a location with a defect.

In addition, logic 150 may determine whether a pixel block thresholdvalue is satisfied by a sum of pixel reflective light intensity valuesreceived from detector 140 for a number of pixels of a pixel block of amulti-layer mask, where the pixel block includes the pixel compared tothe first threshold value. It is considered that the pixel reflectivelight intensity values received by detector 140 for the number of pixelsof the pixel block may each be normalized as described below withrespect to FIG. 3, prior to logic 150 determining whether the secondthreshold value is satisfied. For example, logic 150 may determinewhether the scattered light reflected by multiple pixels around andincluding center pixel CP, when normalized and summed together, satisfya pixel block threshold, to determine whether the pixel block scatters acritical amount of light, such as an amount of reflected light thatwould correspond to a “critical defect” (e.g., such as a selected amountof light appropriate for apparatus 100, substrate 105, and themulti-layers of substrate 105 to satisfy a defect tolerance or thresholdfor a selected critical defect size).

Hence, system 100 may detect abnormalities, bumps, or imperfections inthe planarity or flatness of layers L1 through L5 of substrate 105 asshown in FIG. 2 at a microscopic level (e.g., such as for pixels havinga size of less than 1.0 μm) to identify and locate defects, such aserrant materials or bumps of materials in or on the surface, or layers(e.g., such as layers L1 through L5) of substrate 105 by having logic150 consider bright spots in the dark-field image of scattered ordiffused light reflected from the surface and layers of substrate 120when substrate 120 is illuminated with incident light IL. It is alsocontemplated that logic 150 may be implemented by hardware and/orsoftware, such as digital code or instructions, or a machine-accessiblemedium containing instructions that cause a machine to perform thefunctionality described herein with respect to logic 150.

Surface 115 of substrate 105 may include or define a grid of pixels(e.g., such as grid 300 of FIG. 3 and grid 400 of FIG. 4 as describedbelow), that system 100 inspects, as described herein. Thus, reflectedscattered light intensities may be measured for each pixel of the grid,then a normalized scattered light value may be calculated for each pixelof the grid, then logic 150 may determine whether criteria are met forvarious groups of the pixels of the grid to identify defects within thegrid.

For example, FIG. 3 is a top perspective view of a multi-layer maskblank. FIG. 3 shows an array of pixels, such as grid of pixels 300,center pixel CP, and next pixel NP in direction DIR from center pixelCP. Surrounding center pixel CP is inner perimeter of pixels T1, T2, T3,T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18,T19, T20, T21, T22, T23, and T24. Surrounding inner perimeter of pixelsT1-T24 is outer perimeter of pixels S1, S2, S3, S4, S5, S6, S7, S8, S9,S10, S11, S12, S13, S14, S15, S16, S17, S18, S19, S20, S21, S22, S24,S25, S26, S27, S28, S29, S30, S31, and S32.

According to embodiments, grid of pixels 300 may be pixels on orassociated with substrate 105. For example, grid of pixels 300 may bepixels identified or mapped out with respect to surface 115.Specifically, the pixels of grid of pixels 300 (e.g., such as centerpixel CP, next pixel NP, each of inner perimeter of pixels T1-T24, andeach of outer perimeter of pixels S1-S32) may be pixels having a pixelsize as described above with respect to FIGS. 1 and 2, and may includelayers of a multi-layer patterning mask blank as described herein. Thus,pixels of grid of pixels 300 may correspond to pixels from whichscattered, reflected, or diffused light intensity values or measurementsare made as described herein. For example, system 100 may illuminatepixels of grid of pixels 300 with incident light IL and measurescattered light SL reflected by each pixel, as a result.

More particularly, according to embodiments, system 100, mirrors 120 and130, source 110 and/or detector 140 may include Schwarzschild Optics ordark-field optics that have a magnification of 20×, use an incidentlight wavelength of 13.5 nm, and/or use a detector CCD having a pixelsize of 13.5 μm to measure scattered light from pixels of grid of pixels300. For example, system 100 may detect scattered or diffused light,such as scattered light SL, for a pixel having a width and length ofbetween 0.3 μm and 0.8 μm. Specifically, detector 140 may have a pixelsize of 13.5 μm (e.g., pixel size of detection at detector 140) and the“Schwarzschild Optics” or dark-field imaging optics of system 100 mayhave a magnification of 20×, thus resulting in system 100 being able tosufficiently illuminate a pixel with incident light IL and measure theresulting scattered light SL for a resolution or pixel size as small as13.5 μm divided by 20, or a pixel size equal to 0.675 μm (e.g., a pixelsize of a pixel, such as center pixel CP of FIG. 3). System 100 may alsodetect light from pixels having a size of 0.35 μm, 0.4 μm, 0.45 μm, 0.5μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.8 μm.

Referring to FIG. 3, a normalized light intensity value may bedetermined for center pixel CP by measuring a reflective light intensityvalue (e.g., such as a scattered or diffused reflection light valuemeasured by dark-field imaging optics and/or system 10) for center pixelCP (e.g., such as a reflective light intensity value that includesreflection of incident light IL from the surface as well as layers belowthe surface of substrate 105 at pixel CP) and for at least onesurrounding ring of other pixels. In one instance, reflective lightintensity values for inner perimeter of pixels T1 through T24 are alsomeasured. Likewise, reflective light intensity values for outerperimeter of pixels S1 through S32 are measured. Then, the normalizedlight intensity value for center pixel CP is calculated as thereflective light intensity value measured for center pixel CP divided bythe average of the light intensity values for both the inner perimeterof pixels T1 through T24 and the outer perimeter of pixels S1 throughS32. In other words, (normalized light intensity value for center pixelCP)=(light intensity value for center pixel CP)/((some of lightintensity values for pixels T1 through T24+ some of light intensityvalues for pixels S1 through S32)/56).

It is also contemplated that the denominator of the calculation fordetermining the normalized light intensity value above may instead bethe average of: (1) only perimeter of pixels T1 through T24, (2) onlyouter perimeter of pixels S1 through S32, or (3) one or more shapes orperimeters of pixels other than those shown in FIG. 3. For example, thedenominator of the equation above for determining normalized lightintensity values may be one or more perimeters in the shape of atrapezoid, a rectangle, a square, and a ring of pixels around centerpixel CP. Furthermore, it may be appreciated that the calculationsdescribed above for determining a normalized light intensity value maybe performed on each pixel in grid of pixels 300. For example, theprocesses and calculations described above may be repeated for nextpixel NP, by moving perimeter of pixels T1 through T24 and outerperimeter of pixels S1 through S32 one pixel in the direction ofdirection DIR, and recalculating as described above to determine thenormalized light intensity value for next pixel NP.

Furthermore, according to embodiments, the light intensity values of EUVlight reflected at pixels of grid of pixels 300 may be considered todetermine criteria, such as to determine whether a defect exists in amulti-layered mask blank. For example, FIG. 4 is a top perspective viewof a multi-layered mask blank. FIG. 4 is a grid of pixels having acenter pixel and blocks of pixels including the center pixel. FIG. 4shows grid of pixels 400 having center pixel CP; a first block of fourpixels including center pixel CP; a second block of nine pixelsincluding the first block of pixels; and a third block of twenty-fivepixels including the second block of pixels. For example, reflectedlight intensity values for the pixels of grid of pixels 400 may beconsidered, measured, or determined according to reflected EUV lightintensity values of scattered light, diffused light, or reflected lightresulting from incident light IL, as described above with respect tosystem 100. Moreover, grid of pixels 400 may be a grid of pixels asdescribed above with respect to grid of pixels 300. Consequently, thepixels of grid of pixels 400 may be pixels on substrate 105 or surface115.

According to embodiments, whether a defect exists may be determined byconsidering a reflective EUV light intensity value for center pixel CPand by considering a light intensity value for a block of pixelsincluding center pixel CP and (e.g., such as a block of more than onepixel). It is contemplated that considering the reflected EUV intensitylight value of a pixel includes considering the normalized lightintensity value as described above with respect to FIG. 3. Thus,identifying a defect at center pixel CP of grid of pixels 400 may beperformed by considering whether the normalized light intensity value ofcenter pixel CP qualifies center pixel CP as a candidate of a locationwith a defect, and by considering whether the normalized light intensityvalue of a block of pixels (e.g., such as a block having at least twopixels and including center pixel CP), verifies the criticality of theintensity of the normalized light values of the block of pixels asscattering or diffusing enough light to indicate a critical defect.

According to embodiments, the block of pixels to verify the criticalityof the intensity may be a block of two pixels, a block of three pixels,a block of four pixels, a block of nine pixels, a block of ten pixels, ablock of twenty-five pixels, or a block of thirty-six pixels.Specifically, as shown in FIG. 4, for instance, the block of pixels mayinclude center pixel CP and pixel PB1. Also, the pixel block may includecenter pixel CP, pixel PB1, pixel PB2, and pixel PB3. Moreover, thepixel block may include pixels PB1 through PB3, pixel PC1, pixel PC2,pixel PC3, pixel PC4, and pixel PC5 (e.g., such as with or withoutcenter pixel CP). Additionally, the pixel block may include pixel PD1,pixel PD2, pixel PD3, pixel PD4, pixel PD5, pixel PD6, pixel PD7, pixelPD8, pixel PD9, pixel PD10, pixel PD11, pixel PD12, pixel PD13, pixelPD14, pixel PD15, and pixel PD16; with or without pixels PB1 throughPB3, pixels PC1 through PC5, and/or center pixel CP.

Thus, in one embodiment, it may be determined whether the normalizedscattered or diffused light reflection at center pixel CP satisfies afirst threshold and whether the normalized scattered or diffused lightreflection for the pixel block satisfies a second threshold in order toidentify if a defect is present at center pixel CP, or at the locationof the pixel block. It is to be appreciated that determining whether athreshold value is satisfied may include determining whether a lightintensity value is greater than a threshold value, or greater than orequal to a threshold value.

FIG. 5 is a flow diagram of a process for locating defects in amulti-layered mask blank. At block 510 a substrate is radiated with EUVlight. For example, block 510 may correspond to descriptions above withrespect to radiating or illuminating substrate 105 with incident lightIL. In addition, block 510 may correspond to descriptions of radiatingor illuminating grid of pixels 200 and/or grid of pixels 300 ofsubstrate 105. Moreover, block 510 may correspond to illuminating thesurface and layers below the surface of a multi-layered patterning oretching mask blank as described herein.

At block 520, the light intensity for a first pixel block is measured.Block 520 may correspond to measuring the scattered or diffused lightfor center pixel CP, or a pixel block as described above with respect toFIG. 4. For example, block 520 may include measuring reflected light,detecting reflected light, dark-field image detection, scattered lightreflection measurement, or diffuse light reflection measurement ofincident IL as reflected by the first pixel block as described abovewith respect to FIG. 4.

At block 530, the light intensity value for a second pixel block ismeasured. For example, the second pixel block may correspond to a pixelblock as described above with respect to FIG. 4 and including the firstpixel block, such as where the second pixel block is larger than thefirst pixel block. Block 530 may correspond to measuring light intensityvalues as described above with respect to block 520, but for a secondpixel block as described above with respect to FIG. 4.

At block 540, light intensity values for a third pixel block aremeasured. Block 540 may correspond to measuring light intensity valuesfor a pixel block as described above with respect to FIG. 4, where thethird pixel block includes and is larger than the second pixel block.Measuring light intensity values at block 540 may correspond tomeasuring light intensity values as described above with respect toblock 520, but for a third pixel block as described above with respectto FIG. 4.

At block 550, the light intensity values measured at block 520, 530, and540 are normalized. For example, the light intensity measured for eachpixel of the first, second, and third pixel block may be divided by anaverage of a number of UV light reflection measurements for a number ofpixels surrounding each of the pixels of the first, second, and thirdpixel blocks. In addition, the normalizing of block 550 may correspondto descriptions above for normalizing light intensity values asdescribed with respect to FIG. 3.

At decision block 560, it is determined whether the normalized firstpixel block value or values satisfy or are greater than first thresholdTh1. For example, at block 560, it may be determined whether thenormalized reflected light intensity value of a first pixel block asdescribed for FIG. 4 (e.g., such as of center pixel CP) is greater thanfirst threshold Th1. If at block 560 the normalized first pixel blockvalue or values are not greater than first threshold Th1, then theprocess continues to block 570.

At block 570, it is determined whether the normalized pixel block valuesof the second pixel block are greater than second threshold Th2. Forexample, at block 570, it may be determined whether the normalizedreflected light intensity values for a second pixel block as describedfor FIG. 4 (e.g., such as for center pixel CP plus pixels PB1 throughPB3) are greater than second threshold Th2. If at block 570 the pixelblock values are not greater than the second threshold, the processcontinues to block 590.

If at block 560, the pixel block values or value is greater than thefirst threshold, or if at block 570 the sum of the second pixel blockvalues is greater than the second threshold, then the process continuesto decision block 580. At decision block 580, it is determined whetherthe normalized third pixel block values are greater than third thresholdTh3. For example, at block 580, it may be determined whether the sum ofthe reflected light intensity values for a third pixel block asdescribed for FIG. 4 (e.g., such as for center pixel CP, plus pixels PB1through PB3, plus pixels PC1 through PC5) are greater than thirdthreshold Th3. It is also considered that at block 580 it may bedetermined whether the reflected light intensity values for pixels PD1through PD16, pixels PB1 through PB3, pixels PC1 through PC5, and centerpixel CP are greater than a third threshold.

If at block 580 the sum of the normalized third pixel block values isnot greater than third threshold Th3, then the process continues toblock 590.

At block 590, it is determined that the criteria is not satisfied. Forexample, at block 590, it may be determined that a defect does not existat center pixel CP, at the second pixel block, or at the third pixelblock. Thus, according to FIG. 5, the criteria may not be satisfied wheneither the second or third pixel block fails to meet the second or thirdthreshold, respectively. In other words, decision blocks 560 and 570 maybe used to identify candidates of locations with defects, while block580 may be used to verify whether there is a criticality of scatteredlight intensity by checking the summed intensity within nine totwenty-five pixels around center pixel CP because EUV light scattered bya defect may be imaged in a wide area due to the defect causing a largefield with a curved focal plane within the multi-layers of the maskblank.

If at decision block 580 the sum of the normalized third pixel blockvalues is greater than the third threshold, then the process continuesto block 585. At block 585, it is determined that the criteria issatisfied. For example, at block 585, it may be determined that a defectexists at center pixel CP, at the first pixel block, at the second pixelblock, or at the third pixel block. Furthermore, at block 585, thelocation of the defect, as described above, may be stored (e.g., such asstoring in a memory or register the location or identification of thepixel or pixel block corresponding to the defect).

After block 585 or block 590, it is contemplated that process 500 maymove the location for center pixel CP to a next pixel of a grid ofpixels and inspect the grid of pixels to determine whether a defectexists at or about the location of the next pixel. For example, afterblock 585 or block 590, process 500 may continue and inspect next pixelNP as described above with respect to FIG. 3 (e.g., such as by movingall pixel locations considered one pixel in direction DIR) and thenconsidering new first, second, and third pixel blocks, such as isdescribed above with respect to FIGS. 4 and 5.

In addition, it is contemplated that block 560 may correspond to thefollowing equation:A_(m,n)>Th1   A

wherein A_(m,n) is the normalized reflective light intensity valuedetected at a pixel located at position (m,n) of a grid of pixels (e.g.,such as where m corresponds to a position in the X direction of axes170, and n corresponds to a position with respect to the Y direction ofaxes 170, as shown in FIG. 1); and Th1 represents the first threshold.

Correspondingly, block 570 may correspond to the following equation:

$\begin{matrix}{{\sum\limits_{i,{j = 0}}^{1}A_{{m + i},{n + j}}} > {Th2}} & B\end{matrix}$

wherein A_(m+i,n+j) represent the normalized reflected light intensityvalue at pixels located adjacent to and including pixel A_(m,n), asdescribed above for equation A; and Th2 represents a second threshold.Thus, equation B may represent the sum of normalized reflected lightintensity values for a pixel block.

Next, block 580 may correspond to the following equation:

$\begin{matrix}{{\sum\limits_{i,{j = {- 1}}}^{1}A_{{m + i},{n + j}}} > {Th}} & C\end{matrix}$

wherein A_(m+i,n+j) equals the normalized reflected light intensityvalues for pixels adjacent to or forming a perimeter around pixelA_(m,n), such as is described above with respect to equation A; and Th3is the third threshold. Thus, equation C may represent the sum ofnormalized pixel reflective light intensity values for a block of pixelslarger than the block of pixels summed in equation B, including thepixel block summed in equation B, and/or including pixel A_(m,n).

In the foregoing specification, specific embodiments are described.However, various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of embodiments as set forthin the claims. The specification and drawings are, accordingly, to beregarded in an illustrative rather than a restrictive sense.

1. A system comprising: a source of extreme ultraviolet (EUV) light toilluminate a multilayered patterning mask blank; a first sphericalmirror having a first perimeter and an opening, the first mirror shapedto reflect scattered light to be received from a multilayered patterningmask blank illuminated by the source; a second spherical mirror having asecond perimeter, the second mirror shaped to reflect the scatteredlight received from the first spherical mirror through the opening andto a detector; and a first comparator coupled to the detector to comparea first threshold value to a pixel reflective light intensity valuereceived by the detector for a first pixel of a multilayered patterningmask blank; a second comparator coupled to the detector to compare asecond threshold value to a pixel reflective light intensity valuereceived by the detector for a plurality of pixel block reflective lightintensity values for a pixel block having a perimeter of adjacent pixelsof the multilayered patterning mask blank, wherein the pixel blockincludes the first pixel.
 2. The system of claim 1, further comprising amask blank moving apparatus to move a multilayered patterning mask blankto be illuminated in two dimensions with respect to an axis of the firstspherical mirror.
 3. The system of claim 2, wherein the detectorincludes a charge-coupled device (CCD) camera, and further comprising amirror disposed along the axis to reflect the EUV light from the sourceto the mask blank.
 4. The system of claim 3, wherein an axis of thefirst spherical mirror is perpendicular to a surface of the multilayeredpatterning mask blank.
 5. The system of claim 1, wherein the source ofEUV light is to illuminate a plurality of layers of the multilayeredpatterning mask blank, and the first spherical mirror is to receivediffused light reflections from the plurality of layers.
 6. The systemof claim 1, wherein the source of extreme ultraviolet (EUV) light is toilluminate the multilayered patterning mask blank with EUV light havinga centroid wavelength of between 1.005 and 1.010 times a centroidwavelength of a patterning light to expose portions of a light sensitivematerial on a wafer during a photo-lithographic process, wherein theportions correspond to a pattern to be formed on the mask blank.
 7. Thesystem of claim 6, wherein the patterning light is to be incident upon asurface of the pattern at an angle of between six degrees and 8 degreesfrom perpendicular to the surface, and the first mirror is disposed suchthat an axis of the first spherical mirror is perpendicular to thesurface.
 8. The system of claim 1, further comprising logic circuitrycoupled to the detector to divide the pixel reflective light intensityvalue received by the detector for a pixel by an average of the pixelblock reflective light intensity value received by the detector for aplurality of pixels.
 9. The system of claim 1, wherein the plurality ofpixels of the mask blank form a shape of one of a trapezoid, arectangle, a square, and a ring.
 10. The system of claim 1, wherein thepixel of the multi-layered patterning mask blank is within the perimeterof the plurality of pixels.
 11. The system of claim 1, wherein the firstand second comparator are to compare one of scattered extremeultraviolet (EUV) light reflection measurements and EUV dark-field imagedetections from a multi-layered mask blank.
 12. The system of claim 1,wherein the mask comprises reflective portions of a multi-layeredmaterial and transparent portions.
 13. The system of claim 1, furthercomprising logic circuitry to determine that a criteria indicating adefect in the mask blank at the first pixel is satisfied if one of: thepixel reflective light intensity value received by the detector for thefirst pixel satisfies the first threshold; the pixel reflective lightintensity value received by the detector for the plurality of pixelblock reflective light intensity values for the pixel block satisfiesthe second threshold.
 14. The system of claim 1, wherein the pixel blockis a first pixel block; and further comprising a third comparatorcoupled to the detector to compare a third threshold value to a pixelreflective light intensity value received by the detector for aplurality of pixel block reflective light intensity values of a secondpixel block of the multi-layered patterning mask blank, wherein thesecond pixel block includes the first pixel block and has more pixelsthan the first pixel block.
 15. The system of claim 14, wherein acriteria indicating a defect in the mask blank is satisfied if one of:the pixel reflective light intensity value received by the detector forthe first pixel of the mask blank satisfies the first threshold value;and the pixel reflective light intensity value received by the detectorfor the plurality of pixel block reflective light intensity values forthe first pixel block of the mask blank satisfies the second threshold;and the pixel reflective light intensity value received by the detectorfor a plurality of pixel block light reflective intensity values for thesecond pixel block of the mask blank satisfies the third thresholdvalue.
 16. The system of claim 15, wherein satisfaction of the criteriaindicates a defect in the mask blank at one of the first pixel block andthe second pixel block.
 17. The system of claim 15, wherein the firstpixel block comprises at least two pixels, and the second pixel blockcomprises at least nine pixels.
 18. The system of claim 15, wherein thefirst pixel block is a 2×2 pixel block, and the second pixel block is a5×5 pixel block.
 19. The system of claim 1, wherein the perimeter ofadjacent pixels comprises and outer perimeter of pixels and the firstpixel is surrounded by the outer perimeter of pixels.
 20. The system ofclaim 1, further comprising logic circuitry coupled to the detector tocalculate and average of the pixel block reflective light intensityreceived by the detector for the plurality of adjacent pixels.